1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) display device and a fabrication method thereof and, more particularly, to an OLED display device capable of reducing a bezel width therein and a fabrication method thereof.
2. Description of the Related Art
As the consumer's interest in information displays is growing and the demand for portable (mobile) information devices is increasing, research into and commercialization of light and thin flat panel displays (“FPD”), which substitute cathode ray tubes (CRTs), the conventional display devices, has been actively ongoing.
In the FPD field, a liquid crystal display (LCD), which is lighter and consumes less power, has come to prominence so far. However, the LCD is a light receiving device, rather than a light emitting device, having shortcomings in terms of brightness, a contrast ratio, a viewing angle, and the like, so a novel display device that may be able to overcome such shortcomings has been actively developed.
An organic light emitting diode (OLED) display device, one of novel display devices, is self-emissive, having excellent viewing angle and contrast ratio, and since it does not require a backlight, the OLED display device is lighter and thinner and is advantageous in terms of power consumption. In addition, the OLED display device has advantages in that it is available for DC low voltage driving and has a faster response speed, and also is advantageous in terms of fabrication costs.
Unlike the LCD or a plasma display panel (PDP), a fabrication process of the OLED display device includes only a deposition and encapsulation process, which is, thus, simple. Also, when the OLED display device is driven according to an active matrix scheme having a thin film transistor (TFT) as a switching element in each pixel, although a low current is applied, the same luminance can be obtained, so the LED display device has an advantage in that it can consume less power and high precision and resolution, and can be increased in size.
A basic structure and operational characteristics of the OLED display device will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram explaining a light emission principle of a related art OLED display device.
As shown in FIG. 1, the related art OLED display device includes an OLED. The OLED includes organic compound layers 30a, 30b, 30c, 30d, and 30e formed between an anode 18 as a pixel electrode and a cathode 28 as a common electrode.
The organic compound layers 30a, 30b, 30c, 30d, and 30e include a hole injection layer 30a, a hole transport layer 30b, an emitting layer 30c, an electron transport layer 30d, and an electron injection layer 30e. 
When a driving voltage is applied to the anode 18 and the cathode 28, holes which have passed through the hole transport layer 30b and electrons which have passed through the electron transport layer 30d move to the emission layer 30c to form excitors, and as a result, the emission layer 30c emits visible rays.
In the OLED display device, pixels having the OLED having the foregoing structure, are arranged in a matrix form and selectively controlled by a data voltage and a scan voltage, thus displaying an image.
The OLED display device is divided into a passive matrix display device and an active matrix display device using TFTs as switching elements. Among them, in the active matrix display device, the TFTs are selectively turned on to select pixels and emission of pixels is maintained by the voltage maintained in a storage capacitor.
FIG. 2 is an equivalent circuit diagram of a single pixel in the related art OLED display device. Specifically, FIG. 2 is an equivalent circuit diagram of a related art 2T1C pixel (including two transistors and one capacitor) in the active matrix OLED display device.
With reference to FIG. 2, the pixel of the active matrix OLED display device includes an OLED, a data line DL and a gate line GL which cross each other, a switching TFT SW, a driving TFT DR, and a storage capacitor Cst.
Here, the switching TFT SW is turned on in response to a scan pulse from the gate line GL, thus electrically connecting a current path between a source electrode and a drain electrode thereof. During an ON-time period of the switching TFT SW, a data voltage from the data line DL is applied to a gate electrode of the driving TFT DR and the gate storage capacitor Cst through a source electrode and a drain electrode of the switching TFT SW.
Here, the driving TFT DR controls a current flowing through the OLED according to the data voltage applied to the gate electrode thereof. The storage capacitor Cst stores the voltage between the data voltage and a low potential power source voltage VSS, and then, uniformly maintains during one frame period.
FIG. 3 is a view showing an example of a usage state of the related art OLED display device.
With reference to FIG. 3, a related art OLED display device 1 includes a light emission region 3 including an OLED and a circuit unit 30 electrically connected to a printed circuit board (PCB) and transferring a signal transferred from the PCB to the light emission region 3.
The light emission region 3 outputs a display image according to a signal received from the PCB through the circuit unit 30.
The related art OLED display device 1 includes an external appearance glass 2 attached on a front surface thereof so as to be used in a mobile communication terminal or an information terminal such as a digital TV, a computer, or the like, and in general, a space between an outer side of the external appearance glass 2 and the light emission region 3 is called a bezel width W′.
FIG. 4 is a plan view schematically showing the bezel region in the OLED display device illustrated in FIG. 3.
With reference to FIG. 4, in the related art OLED display device, the light emission region 3 displaying display information is formed on a substrate 10, and a plurality of pixels (not shown) of an OLED are formed in the light emission region 3.
Here, a gate driving circuit unit 14 is positioned on the side of the light emission region 3 and electrically connected to the PCB (not shown) to receive an external signal.
A sealant 40 is formed at an outer side of the gate driving circuit unit 14 to protect the gate driving circuit unit 14 and the light emission region 3 against impurities such as external moisture, oxygen, and the like.
A wiring region 5 in which a power (GND) wiring (not shown), an ON/OFF switch wiring (not shown), a reference wiring (not shown), or the like, are disposed is positioned between the gate driving circuit unit 14 and the light emission region 3.
As mentioned above, the space between an outer side of the substrate 10 and the light emission region 3 is called the bezel width W′, and when the bezel width W′ is large, dead spaces of the information terminal such as a mobile phone, or the like, is increased, defiling the outer appearance or design.
In particular, when the OLED display device is fabricated, a horizontal power wiring is led into the light emission region 3 by using portions of the left and right bezels. Here, in case of configuring a power source led in the horizontal direction using the left and right bezels, the additionally wiring region 5 is required in the bezel region in order to supply power, resulting in an increase in the bezel width W′.
Namely, as the OLED display device is advancing toward high resolution, layout of the power wiring such that the power wiring is led into the light emission region 3 in a vertical direction is not possible, so the power wiring is required to be designed in a horizontal direction within the pixel. Here, however, when the power wiring led into the light emission region 3 is horizontally disposed, the power wiring should be designed in the left and right wiring regions 5 by using a metal for a data wiring or a gate wiring, increasing the width Y′ of the wiring regions 5, namely, the bezel width W′.